Nitric acid concentration



y 1933- l. HECHENBLEIKNER ET AL 1,916,837

NITRIC ACID CONCENTRATION Filed May 9, 1950 2 Sheets-Sheet l CONCENTRATED SULPHURIC ACID DILUTE NITRIC ACID CONCE- TRATED NITRIC 67 iii! INVENTORS INGENUIN HECHENBLEIKNER SAMUEL F. SPAN ER TO SULPHURIC ACID CONCENTRATO DILUTE SULPHURIC AClD July 4, 1933. HQHECHENBLEIKNER Er AL 1,316,837

NITRIC ACID CONCENTRATION Filed Hay 9, 1930 2 Sheets-Sheet 2 INVENTORS INGENUIN HECHENEJLEIKNER SAMUEL F. SPAN ER AT'roRNEYs cyr I NORTH CAROLINA.

Patented July 4, 1933 UNITED,

INGENUIN HECHENBLEIKN OF @HARLDTTE, NORTH CAROLINA, AND SAMUEL F.

SPANGLER, 0F PHILADELPHIA, PENNSYLVANIA, ASSIGNORS TE) CHEMICAL CON- STRUCTION CORPORATION, OF CHARLOTTE, NGR'EH GARQLINA, A CORPQRATION -433i Application flied stay 9,

This invention rel-ates to nitric acid con centration by the use of a deb drating agent, such as sulphuric acid, "an to apparatus therefor.

in copending applications of lngenuln llechenblei'kner, one of the present applicents, Serial No. 256,561, filed February 24,-

retained in the tubes by the use of dams utthe discharge ends thereof. The Water content of the nitric acid is, in the main, removed by the sulphuric acid, although some Water vapor may incidentally be distilled 011i? vvith the nitric acid vapor.

.lt hes been found difdcult to obtain nitric acid of very high concentration from such an arrangement, particularly so when operating the same at commercial capacities, by which mean e capacity or output which. will justify the cost of installation of such 5. concentration system comparison with other kinds of conc ntration systems. The primer-y object of the present invention is to retain compactness or floor space economy of the aforesaid system, end at the same time to so elter system end the method of op.- eretion oi that as large yield of concentrnted nitric ucid iney be ob-= 'teined.

To end. we odd to vertically super posed group o conn cted retort tubes dehydrating tower connected to the uppen most tube. The sulpnuric acid, utter Slowing downwardly through the dehydroting tower,

mired the dilute nitric acid, and the ecid mixture iloivs through the retort The cold mixture in such of the tubes is ltept its boiling point in order to evolve nitric ncid vapor, and this, together with sonic water vapor incidentally driven 05 from scid niixture at the same time, flows out of the retort system into the dehydrating tower music new cononnrnn'rron -into. Serial lie. stasis.

whereeny such Water vapor is removed from nitric acid vepor by the sulphuric acid descending in the tower. it will thus be seen that in the present arrangement the dehydrating function of the sulphuric acid is em= 'ployed doubly, primarily to remove Water from the dilute nitric acid liquid, and seconderily, to remove water vapor from the concentrsted nitric acid vapor. v

its has already been indicated, a quantity of sold mixture is retained in such of the retort tubes by it damn at the discharge end thereof. The space above the liquid content being open, it continuous passage for the iiow of vapor upward through the retort system is provided. lVe have found it desirable to make the level of the liquid retained in each or the retort tubes adjustable, so the quantity or" acid mixture in any of the tubes my be determined independently of the level established in the other tubes. For this purpose We provide means for adjusting the liquid content in each of the tubes independently of the other tubes, and this means most simply consists oi interchangeable and adjustable dams inserted at the discharge end or the tubes. The most desirable levels be employed may be determined empiricslly and experimentally, end generally spealzinc, we it dcsirnble to reduce the depth or acid mixture in the upper tubes relative to that in the lower tubes. Presumably this results from the fact that the quantity of evolved gee owing through the tubes increases cumula reached, and proves desirable to increase the allowed for hot the evolution of ely as the upper tubes are he tube in question end the pesssge oi; gee iof the preceding or lower tunes. A

the concentration system disclosed in the applications of lngenuin l-lechenbleilrner the'retort tubes ere heated by steam jacliem ell supplied with steam from a common supply pipe. This, theoretically, tends hold the temperature applied externally to the tubes constant, but inasmuch as considerable heat is liberated in the upper tubes simply as a result of the mixing of the sulphuric and r nitric acids, the final temperatures in the retort tubes, and unless this is done, the degreeof denitration is decreased, and excessive osses of the retort tubes de are caused. Inasmuch as the acid mixture in each of the retort tubes differs from that the other tubes, the boiling temperaturesalso difier.

Accordingly still another object of our invention res1 es in the provision of independent means to heat-the retort tubes so that the temperature in at least some of the tubes may be controlled indegzndently of the temperature in the other tu s. In the particular system here disclosed, this is accomplished by the use of individual'steam jackets for each of the tubes, and individual steam supply pipes connected thereto, so that the pressure and consequently the temperature in each of the tubes may be controlled independently of that in the other tubes.

To insure uniform operation, it is necessary that the nitric and sul huric acids be well mixed and not rmitteti to stratify in la ers,

and to accomp ish this is still another 0 ject of our invention. Thorough mixing may readily beobtained if accomplished in a large volume of liquid and, accordingly, we keep the level of the acid mixture in the uppermost tube relatively high. However, to permit sufiicient space for the passage of gas from the lower tubes, it is desirable to reduce the evolution of gas within this tube. Also, the heat of mixing of the acids is greatest at this oint, and. we find that considerable distilation of nitric acid vapor may be obtained.

as a result of this heat alone. An important feature of our invention resides in the discovery that the first tube may be left unheated, and that improved operatin efiicienc'y may be obtained thereby. In e ect, therefore, we (provide between the system of retort tubes an the dehydrater, an additional tube which we call a mixer tube.

The evolution of nitric acid va or in each temperature maintained therein, but also upon the length of time during which a given quantity of acid mixture is exposed to that temperature. This, ultimately, is a factor of the velocity of flow of acid mixture throu h the system which, in turn, depends u on e output or capac1t of the system and e cross sectional areao the tubes, assumin as is nerall the case, that approximate y simiar portions of the various nds not 0 y upon the tubes are useldfor specifically, we find that the system should be provided with tubes having a cross sectional area of from 5 to 20 and preferably about 8 square inches per ton of nitric acid manufactured daily.

The dehydrated nitric acid vapor leaving the dehydrating tower is passed throu h an appropriate condenser, in which it is iquefied and finally collected as the desired concentrated nitrlc acid. We prefer to locate the condenser directly above the retort tubes inasmuch as this arrangement is the most economical of floor space. However, the addition of a condenser and a dehydrating tower to the bank of retort tubes causes the structure to assume considerable height, and to economize in ceiling height as well as floor space is another ob ect of the present invention. To accomplish this, we' arrange the horizontal retort tubes in zigzag vertical superposition rather than simple linear vertical superposition. In this manner the nec essary hei ht of the bank of retort tubes and of the ban of condenser tubes may each be halved without in any way sacrificing the dc -sirable features of simplevertical superposi- To the accomplishment of the foregoing and such other objects as will hereinafter appear, our invention consists in the nitric acid concentration method and apparatus as here inafter are more particularly described in the specification and sought to be defined in the claims. The s ification is accompanied by drawings in w ich:

Fig. 1 is a front elevation of a nitric acid concentration system constructed in accord- The dilute nitric acid to be concentrated flows from a tank N into the tube M in which it is mixedwith the sulphuric acid. Theacid mixture flows downwardly through a vertically superposed bank of retort tubes R heated by individual steam jackets. Separate bodies of acid mixture of diflerent strengths are retained in the retort tubes by dams located at the discharge ends thereof, such a dam being shown in Flg. 4, and its mode of a plication to the retort tube being shown in ig. 8.

Nitric acid vaporis evolved from the-acid mixture in each; of the retorttubes, and this s considerehl The dehydrated nitric acid vapor flows from the top of thetower downwardly through interconnecting pipe 3? end then upwardl through a bleocher pipe B and into s has of water jacketed condenser tubes (1 in which the nitric acid vapor is condensed to e'liquid which flows beck down through hleecher pipe B in which it is loleeehed by the rising nitric ecid vapor, and thence into at water jacketed collecting tube 1 from which the concentreo ed nitric acid is led to any suitable storage teach. v

@onsidering' the system more in detail, tank S is supplied. with warm SltlPlil'lllilC ecid having a strength of from 88 $1743 end the rote ofiiow thereof downwerdly through {pipe and distrihutihgno'zzle the deiydreting tower D is controlled by any suit able reguletihgdevice or valve =6. The dehydrating tower D is only pertielly, so hell", tilled with it loose pecking such es s soirel rings over which the stil ohuric sci discharged the nozzles through which the scid trickles e 1 into smell in order to melee contect with ii' 'iic acid end wetter yopors rising iipwt The so iiows vided h tithe oe coiiceiitroted having; from the valve i s "(iii 2C case, the o M i 3 the some From the rower tuloe the acid flows given in Fig. 4, referringto which the dam 20 is rovided with a, smooth rim 22 castintegra y therewith so that the dam may be clamped between the fittings at the end of the retort tube. The dam 20 may also be provided with a tiny aperture 24 at the lowermost edge thereof through which the "liquid content of the retort tubes may drain when the lent is shut down-for any reason. Dams, suc 1 as that illustrated in Fig. 4: may be provided, in which the overflow edge or lip 26 is at different heights so that the level of ii iiid in one retort tube may be determine independently of the level in the other tubes. It should also be noticedthat the rim22'is not provided with bolt holes or the like, and that the dam may therefore be turned es desired before locking the some between the fittings at the end of the retort tube. This titting of the dam may he used to very the let el of liquid maintained in the retort tubes when it is not desired to remove the dam for replacement by another.

llie manner in which the dam is located and functions is clearly evident from Fig. 3 in which a retort tube such as the tube l+lis connected to the next succeeding retort tube through ipe elbows 28 30. The rim 2:2 of the Jam is clomped between the tube it and the elbow 28 when the flanges 32 and 34, respectively located on the tube it end the elbow 28, are clamped together, preferably by clamping colts not shown in the drawings. A blank ring 36 is clamped between tuhe end the elbow 330 in 'der to specs the some correctly when account of the dam 3: 1 the mixer tube and the manner of olociog the some have not bee. described in oil bees-use eferohly do coin de already given 1 as done in at uni 3 throughout 't the problem.

, :6} replacement l steam jackets which surround the retort tubes and which may be mounted thereon in any conventional manner, such as that illustrated in Fig. 3. Referring to that figure, the

; lead to steam jacket 38 has attached thereto at each end a collar 40 with, which a gland 42'cooperates so as to compress packing 44 around the retort tubei14, and thereby prevent leakage of steam from the jacket.

Reverting to Figs. 1 and 2, the steam jackets for the tubes 11-17 are each supplied with steam from separate steam pipes respectively numbered 51-57. The pressure of the steam supplied to each of the jackets may be regulated, and consequently the temperature and heat applied to the various tubes. The condensed steam from the jackets is drained through drain pipes 61-67 which appropriate trap means for ermitting the ischarge of water but not 0 steam. In the case here illustrated, the steam pressure supplied to the tubes ranges .from about 190 to 240 pounds, the highest pressure hemg applied to the tube 17. It will be understood that the steanrjackets of the retort tubes may be arranged in a plurality of groups, the steam pressure supplied to each ofwhich is regul'atable independently of the other groups, instead of employing the ultimate arrangement here illustrated in which. each steam acket may itself be independently controlled. It should further be understood that the retort tubes may be heated by means other than steam jac et's, as, for example, electrical heating by resistance or by induction, so long as the requirement that the temperature a plied to some of the tubes be controllable in ependentl of the temperature of the other tubes is in filled.

The nitric acid content is distilled off in the successive retort tubes, and the residual sulphuric acid, which is practically free of all nitric acid, flows from the retort tube 17 into a sulphuric acid cooler 70, from which it is re-concentrated to a stren h suitable for reeated usein the sulphuric acid supply tank The residual sulphuric acid in the cooler 70 may have a strength of, say, 72 to 76% and a nitric acid content of less than .3%. This acid is concentrated to about 88 to 91% before being returned to the sulphuric acid supply tank SQ The nitric acid vapor distilled in the retort and mixer tubes,"together with some water vapor evolved therewith, flows upwardly throughthe tubes and through the dehydrating tower D. The descendin sul huric acid removes the water vapor, an the ehydrated nitric acid vapor'fiows out of the top of. the

- tower and into the condenser C. A bleacher pipe B is provided between the tower D and the condenser C, and to conserve ceiling height the bleacher pipe 13 is located alongside of, rather than above the tower D. The

nitric acid vapor leavin the tower is there-- tone first led downwar y through the pipe P before enterin and ascending in 1 the bleacher pipe B. e operation of the latter is explained subsequent y.

Fromthe bleacher pipe B the nitric acid gas flows into the condenser d made up of water jacketed tubes connected in series and arranged in vertical superposition in a manner uite similar, to the retort tubes 1117, but t 1e condenser-.tubes are not rovided with dams, and the jackets are sup ied with cooling water rather than heat. he coolin water is admitted through pipes 72 an discharged from pipes 7 1 so that the water and vapor are in counter-flow relation, and the design is such that all of the acid is condensed by the time the end of the condenser is reached A suction fan 76 is connected to the outlet of the condenser C and draws undissolved lower oxides of nitrogen, together with air which may have leaked into the system, out

of the retort tubes, dehydrater, and condenser. Uncondensed nitric acid vapor will also be drawn off by the fan 76, but in normal pressure even in the lowermost retort tube should be slightly negative, and, while it is possible to operate a plant with a slightly positive pressure at this point, any increase in positive pressure results in a strong nitric acid content in the residual sulphuric acid discharged from the retort tubes. It may be pointed out at this time that the bleacher pi e B is preferably left without packing, and t e dehydrating tower D is only'partially filled with a very loosepackin in order not to cause too great a pressure di erential between the retort tubes R and the condenser C, or, differently expressed, in order to permit of the desired vacuum in the retort R without so great a vacuum in the condenser C as will in juriously afiect the condensation in the same.

The nitric acid condensed therein flows downward through the condenser tubes C and then descends in the bleacher pipe B where in it is exposed to the rising current of hot' acid vapor which drives ofi' lower oxides of nitrogen dissolved in'the descending acid, theaeby bleaching or clearing the color of the aci The bleached acid'flows into the water jacketed tube T, after which it is led to a conduit 80 ruining to any suitable storage tank lid ' upturned pipe circuit 82, so arranged that the tube T iskept full of acid. This volume of acid is considerably warmer at the intake than at the discharge and of the tube T, so that residual oxides of nitrogen may still be driven oil therefrom and upward into the bleacher pipe B. The final product is a clear, concentrated nitric acid having a strength of about 97%. 7

It has previously been explained that in our retort arrangement each of the retort tubes constitutes in effect a retort independent of the other tubes, for each tube has its own body of acid mixture which is not in direct solution contact with the acid mixture in the other tubes, and the liquid level and operating temperature in each tube is adjusted for optimum results, taking into con sideration the strength of acid mixture in the particular tube, and the relation of the tube to the preceding and succeeding tubes. However the evolution of nitric acid vapor is a function not only of temperature but also of time. The present .process being a continuous one the time of exposure. in each retort tube depends upon the velocity of flow of mixture therethrough which in turn dc' pends upon the capacity or outputat which the system is operated and the cross sectional area of the tubes. We find that the cross sectional area of the tubes must be made sufiiciently great relative to the desired output to keep the flow velocity through the tubes down to a value giving optimum yield. Our experiments indicate that a cross sectional area of from 5- to 20 square inches per ton of nitric acid manufactured daily is satisfactory with a system" like that here disclosed and that a cross sectional area of about 8 square inches per daily ton is a preferable value.

Too small a cross sectional area of tubercsults in a poor degree of denitration and may cause the tubes to buck one another. In an already existing plant this factor becomes of importance in determining the most economical capacity at which the vplant is to be operated. In the case of a prospective plant being designed this quantity becomes important in determining the selection of the tube diameter to be used for a desired plant capacity. I

lit will be obvious from an inspection oi the drawings that our arrangement is ex cccdingly economical or door space, because the hauls oi retort tubes it is arranged verti= cally, the hauls of? condenser tubes Cis also till vertically, and the dehydrating tower D is placed in vertical alignment there with, ldowever, this arrangement becomes quite in height, and one step to economize in W ng height has already been mentioned, ""1 L at the bleacher pipe B placed u oi instead of in vertical alignment with the dehydrating tower D. Another way in which we economize in ceiling height is the zigzw vertical superposition of the retort and condenser tubes 1n contrast with a simple vertical alignment. This zignag arrangement is very clearly shown in Fig. 2 and hardly needs explanation. It will be clear from an inspection of the drawings that the height of each bank of tubes may readily be halved, and meanwhile ample room is provided for standard elbows and fittin and the latter are all perfectly accessib e and readily removable to permit of the removal and replacement of one of the tubes without disturbin the other tubes. The sli htl added wi th of each be of tubes is of itt e consequence, inasmuch as this additional width would anyway he needed for various accessories such as the dehydrating tower D, and the like.

In the appended claims we shall refer to the tubes as being in vertical superposition, intending thereby to include the case in which the tubes are arranged all in one vertical plane, as well as the more specific resent case inwhich the tubes are arrange in zigza vertical superposition or in two vertica lanes, because both arrangements are generreally alike when contrasted with an arrangement in which the tubes are placed in horiaontalcollateral relation, or in a step or stairway formation.

The manner of constructing and operatin the nitric acid system of our invention wil it is believed, in the main be apparent from the foregoing description thereof. The use of tubes arranged in zigzag vertical su erosition economizes in floor space and cei ing lieight, and permits of the acid mixture in each of the retort tubes 'bemg kept isolated from that in the other tubes. Removal of the water vapor distilled from the acid mix ture, along with the nitric acid vapor in a separate dehydrating tower permits each of the retort tubes to be operated under the most favorable conditions for distilling the desired vapor therefrom, and each or the tubes is arranged for independent adjustment of the liquid level and the temperature therein, so that these optimum conditions may be provided. The mixer tube insures thorough mixing of the sulphuric and nitric acids, and at the same time takes advantage oil the solu= tion heat oil the mixture. The size of retort tee tube is selected in its relation to the desired plant output for bat flow velocity and consequent denitraion, general, the degree of purity oil concentration of the product nitric acid increased.

will he that while we have shown. and described our invention the preferred form, modifies tions he made in the method and system disclosed without departing trone'the spirit Ill) lltl

a mixture in each of of the invention, defined in the following claims' We claim: 1. In the operation of a-nitric acid separator or/and concentrator comprising a series of heated retort tubes, the method which.

includes mixing the dilute nitric acid with sulphuric acid and passing the resulting acid mixture through the retort tubes, and independently controlling the level of the acid t.1e retort tubes relative to the levels in the other tubes in order to obtgin the most favorable evolution of nitric ac1 2. In the operation of a nitric acid separator or/and concentrator comprising a series of retort tubes, the method which includes mixing the dilute nitric acid with sulphuric acid and passing the resultin acid mixture through the retort tubes, an independently controlling the temperature in each of the retort tubes relative to the temperatures in'the other tubes in order to obtair the most favorable evolution of nitric ac1 3. In the operation of a nitric acid concentrator comprising a series of retort'tubes, the method which includes mixing the dilute nitric acid with sulphuric acid and passing the resulting acid mixture through 4 the retort tubes, controlling the flow velocity through the retort tubes, and independently controlling the acid level and the temperature in each of the tubes relative to the levels and temperatures in the other tubes in order to obtain the most favorable evolution of nitric acid.

4. A nitric acid separation or/and concentration system comprising a plurality of vertically superposed retort tubes connected in series and each provided at its discharge end with a dam, a relatively short dehydrating tower connected thereto, a sulphuric acid 'suppl tank arranged to cause sulphuric acid flow t rough the dehydrating tower and into the retort tubes, a supply tank for dilute nitric acid connected to the retort tubes below the tower and means to heat the retort tubes.

5. A nitric acid separation or/and concentration system comprising a plurality of vertically su erposed retort tubes connected in series an each provided at its discharge end with a dam, a relatively'short and loose- I packed dehydrating tower connected to t e uppermost tube, a condenser connected to the dehydrating tower, suction means connected to the condenser, a sulphuric, acid suppl tank arranged to cause sulphuric acid flow downwardly through the dehydratin tower and into the retort tubes, a supply ta for dilute nitric acid connected to the retort tubes below the tower, and means to heat the retort tubes.

6. A nitric acid separation or/and concentration system comprising a substantially horizontal mixer tube and a plurality of vertically superposed retort tubes all connected in series and each provided at its discharge end with adam, a deb drating tower connected to the mixer tulze, a sulphuric acid s p y; flow t rough the dehydrating tower and into the mixer tube, a supply tank for dilute nitric acid connected to the mixer tube, and means to heat the retort tubes.

. 7 A nitric acid separation or/and con centration system comprising a substantially ,horizontal mixer tube and a plurality of vertically superposed retort tubes all connected in series and each rovided at itsdischarge end with a dam, a loosely packed dehydrating tower connected to the mixer tube, a condenser connected to the dehydrating tower, suction means connected to the condenser, a sulphuric/acid supply tank arranged to cause sulphuric. acid flow downwardly through the dehydrating tower and into the mixer tube, a supply tank for dilute nitric acid connected to the mixer tube, and means to heat the retort tubes but not the mixer tube.

8. A nitric acid separation or/and con centration system comprisingamixer tube and a plurality of vertically superposed retort tubes all connected in series and each provided at its discharge end with a dam, a dehydrating tower connected to the mixer tube, a condenser connected to the top of the dehydrating tower through an upright bleacher pipe means to drain nitric acid from the bottom of the bleacher pipe, suction means connected to the condenser, a sulphuric acid supply tank arranged to cause sulphuric'acid flow downwardl through the dehydrating tower and into t e mixer tube, a supply tank for dilute nitric acid connected to the mixer tube, and means to heat the retort tubes.

9. A nitric acid separation or/andconcentration system comprising a plurality of re.- tort tubes all connected in series and each provided at its discharge end with a dam, a dehydratin tower connected thereto, a sulphuric aci su ply tank arranged to cause sulphuric acid ow through the dehydrating tower and into the retort tubes, a supply tank for dilute nitric acid connected to the series of retort tubes, and independent means to heat the several retort tubes so that the temperature in some of the tubes may be controlled independently of the temperature in the remainin tubes.

v 10. A nitr1c acid separation or/and concentration system comprising a plurality of vertically superposed retort tubes all connected in series and each provided at its discharge end with a dam, a dehydrating tower connected to the uppermost tube, a condenser connected to the dehydrating tower, a sulphuric acid supply tank arranged to cause sulphuric acid flow downwardly through the dehydrating tower and into the retort tubes,

tank arranged to cause sulphuric acid.

' a supply tank for-dilute nitric acid connected to the series of retort tubes, and means to heat the retort tubes comprising individual steam jackets for each of the tubes and individual steam supply pipes connected thereto so that the temperature in each of the tubes may be controlled independentlyof the temperature in the remaining tubes.

11. A nitric acid separation or/and concentration syste including a plurality of vertically superposed substantially horizontal retort tubes connected in series, and means for adjustin the liquid content in each of the tubes in ependently of the other tubes.

12. A nitric acid separation or/and concentration system including a plurality of vertically superposed substantially horizon tal retort tubes connected in series, and means for adjusting the liquid content in each of the tubes independently oi the other tubes comprising an adjustable dam inserted at the discharge end of each of said tubes, said dams being so adjusted that the liquid content is greater in the lower than in the higher tubes.

13. A nitric acid separation or/and con centration system including a plurality of vertically superposed substantially horizontal retort tubes connected in series, means the tubes independently of the other tubes, and independent means to heat the several retort tubes so that the temperature in some of the tubes may be controlled independently of the temperature in the other tubes.

14. A nitric acid separation or/and coni centration system comprising a plurality of vertically superposed retort tubes connected till '- and into the retort tubes,

in series, means for adjusting the liquid content in each of the tubes independently of the other tubes, a dehydrating tower connected thereto, a sulphuric acid supply tank arranged to cause sulphuric acid flow through the dehydrating tower and into the retort tubes, a supply tank for dilute nitric acid connected to the series of retort tubes, and means to heat the retort tubes,

15. A nitric acid seperation or/and concentration system comprising a plurality of vertically superposed retort tubes connected in series, means for adjusting the liquid content in each of the tubes independently of the other tubes comprising an adjustable dam insorted at the discharge end of each of said tubes, at dehydrating tower connected to the uppermost tube, a condenser connected to the dehydrating tower, a sulphuric acid supply tank arranged to cause sulphuric acid flow downwardly through the tower supply for l We retort dilute nitric acid connects tubes, and means to it, A nitric acid centration system comp vertically superposed r for adjusting the liquid content in each of in series, meansfor adjusting the li uid content in each of the tubes indepen ently of the other tubes, a dehydrating tower connected to the uppermost tube, a sulphuric acid supply tank arranged to cause sulphuric acid flow downwardly through the dchydratand a plurality of retort tubes all connectedin series and each provided with means for adjusting the liquid content in each oi the tubes independently of the other tubes, a dehydrating tower connected to the mixer tube,

a sulphuric acid supply tank arranged to cause sulphuric acid flow downwardly through the dehydrating tower and into the mixer tube, a supply tank for dilute nitric acid connected to the mixer tube, and independent means to heat the retort tubes so that the temperature in some of the tubes may be controlled independently of the temperature in the other tubes.

18. A nitric acid separation or/and concentration system comprising a mixer tube and a plurality of vertically superposed retort tubes allconnected in series and each provided with means fol adjusting the liquid content. in' each of the tubes independently of the other tubes, a dehydrating tower connected to the mixed tube, a condenser connected to the top of the dehydrating tower through an upright bleacher pipe, means to drain nitric acid from the bottom of the bleacher pipe suction means connected to the condenser, a sulphuric acid supply tank arranged to cause sulphuric acid flow downwardly through the dehydrating tower and into the mixer tube, a supply tank for dilute nitric acid connected to the mixer tube, and independent means to heat each of the retort tubes so that the temperature in each of the tubes may be controlled independently of the temperature in the other tubes.

19. A nitric acid separation or/and concentration system comprising a mixer tube and a plurality of vertically superposed retort tubes all connected-in series and each provided at its discharge end with an independently adjustable dam for adjusting the liquid content in each of the tubes independently of'the other tubes, a dehydrating tower conected to the mixer tube, a condenser connected to the .top of the dehydrating tower through an upright bleacher pipe,

bleacher pipe suctionv means connected condenser, a sulphuric acid supply ranged to cause sulphuric acid flow downwardly through the dehydratmg tower and into the mixer tube, a supply tank for dllute nitric acid connected to the mixer tube,.and

' of the tubes may be controlled independently of the temperature in the other tubes.

'20. A nitric acid separation or/and concentration system comprising a plurahty of horizontal retort tubes connected in series and arranged in zigzag vertical superposition when considered in side elevation and also when considered in end elevation, in order to conserve both floor space and ceiling height, each of said tubes being (provided with means for adjusting the liqui content in each of the tubes independently of the other tubes.

21. An nitric acid separation or/and concentration system comprising a plurality of horizontal retort tubes connected in series and arranged in zigzag vertical superposition when considered in side elevation and also when considered in end elevation in order to conserve both floor space and ceiling height, each of said tubes being provided. at its dicharge end with an independently adjustable dam for adjustin the liquid content in each of the tubes in ependently of the other tubes. 7

22. A nitric acid separation or/and concentration system comprising a plurality of retort tubes connected in series and provided at their discharge ends with. means for obstructing and retaining a body of liquid therein, a dehydrating tower connected to said series of retort tubes, and means t heat said tubes. i

23. A nitric acid separation or/and concentration system comprising a mixer tube and a plurality of retort tubes connected in series and provided at their dischar e ends with means for obstructing and retaining a body of the liquid therein means to heat the retort tubes, and a dehydrating tower conneeted to the mixer tube.

24. A nitric acid separation or/and concentration system including a plurality of retort tubes connected in series, and means for adjustin the liquid content in each of the tubes in ependently of the other tubes.

25. In the o eration of a nitric acid separation or/an concentrator comprisin a series of heated retort tubes, the met 0d which includes mixing the dilute nitric acid with sulphuric acid and passing the resultin acid mixture through the retort tubes, in ependently controllin the level of the acid mixture in each of t e retort tubes relative to the levels in the other tubes in order to obtain the most favorable evolution of nitric acid, and passing the resulting nitric acid vapor and the water vapor evolved therewith in counter-current relation to the SlllPllllIlC acid going into the acid mixture.

26. In the operation of a nitric acid sepa rator or/and concentrator comprising a series of retort tubes, the method which includes mixing the dilute nitric acid with sulphuric acid and passing the resulting acid mixture through the retort tubes, independently controlling the temperature in each-of the retort tubes relative to the temperatures in the other tubes in order to obtain the most favorable evolution of nitric acid, and passing the resulting nitric acid vapor and the water vapor evolved therewith in countercurrent relation to the sulphuric acid going into the acid mixture.

27. In the operation of a nitric acid separator or/ and concentrator comprising a series of retort tubes, the method which includes mixing the dilute nitric acid with sulphuric acid and passing the resulting acid mixture through the retort tubes, controlling the flow velocity through the retort tubes, independently controlling the acid level and the temperature in each of the tubes relative to the levels and temperatures in the other tubes in order to obtain the most favorable evolution 4 of nitric acid, and passing the resulting nitric acid vapor and the water vapor evolved there,-

with in counter-current relation to the sul:-

phuric acid going into the acid mixture.

28. A denitration system for the separation of nitric acid from a mixture of liquids, comprising a mixer tube and a plurality of retort tubes all arranged substantially horizontal and all connected in series and each provided" at its discharge end with means for obstructing and retaining a body of .theliquid mixture therein, means to create "a marked difference in temperature between the retort tubes on the one hand and the mixer tube on the other hand, the retort tubes j being kept at hightemperature, and a dehydrating tower connected to the mixer tube.

29. A denitration system for the se aration of nitric acid from a mixture of ii uids comprising a mixer tube and a plura it of retort tubes all arranged substantially horizontally and all connected in series and each provided at it's discharge end with means for obstructing and retaining a body of the liquid mixture thereinfmeans to heat the retort tubes but not the mixertube, and a dehydrating tower connected to the mi ger tube.

Si ed by said Inemnum Hmmnnmmrxiwm at arlotte, in the county of Mecklenburg and State or North Carolma this-26 day of April A. D. 1930. i

INGENUIN HECHEN'BLEIKNER.

Signed by said- SAMUEL F. SPANGLER at Buffalo, in the county of Erie and State of New York this 29th day of A ril A. l). 1930.

' SAMUEL F. rPANGLER, 

